Basis of Presentation - Schedule of Basic and Diluted Earnings Per Common Share Calculation (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Basic earnings per common share:
Net income applicable to FB Financial Corporation	$ 120,224	$ 124,555	$ 190,285
Dividends paid on and undistributed earnings allocated to participating securities	0	0	0
Earnings available to common shareholders	$ 120,224	$ 124,555	$ 190,285
Weighted average basic shares outstanding (in shares)	46,781,214	47,113,470	47,431,102
Basic earnings per common share (in dollars per share)	$ 2.57	$ 2.64	$ 4.01
Diluted earnings per common share:
Earnings available to common shareholders	$ 120,224	$ 124,555	$ 190,285
Weighted average basic shares outstanding (in shares)	46,781,214	47,113,470	47,431,102
Weighted average diluted shares contingently issuable (in shares)	41,578	126,321	524,778
Weighted average diluted shares outstanding (in shares)	46,822,792	47,239,791	47,955,880
Diluted earnings per common share (in dollars per share)	$ 2.57	$ 2.64	$ 3.97
Restricted Stock Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Restricted stock units outstanding considered to be antidilutive (in shares)	172,677	11,888	4,400